1. Field of the Invention
The present invention relates to a security technique employable in communications.
2. Description of the Related Art
In wireless communications, encryption techniques are preferably used to avoid any wire tapping. Various encryption methods, such as for example WEP (Wire Equivalent Privacy), TKIP (Temporal Key Integrity Protocol), and AES (Advanced Encryption Standard), can be used in wireless LAN communications performed according to the IEEE802.11 standard.
Also, Counter mode with Cipher-Block Chaining-Message Authentication Code Protocol (also known as CCMP) is usable to detect alteration (for example falsification) of AES data according to the IEEE802.11i standard.
According to the CCMP, a wireless communication device can encrypt transmission data using a packet number which is incremented for each packet. Other communication devices can decrypt a received packet with reference to the packet number used in the encryption of the data, and can detect alterations present in the received encrypted data.
An infrastructure mode and an ad-hoc mode are two communication modes provided by the IEEE802.11 standard. In the infrastructure mode, wireless communication devices can communicate with each other via an access point (AP). In the ad-hoc mode, the wireless communication devices can directly communicate without using the AP.
As described above, the encryption processing according to the CCMP is performed based on the packet number. Therefore, the encryption key is differentiated for each packet.
In the infrastructure mode, the AP has a function of administrating the packet number of each wireless communication device in the network to establish data communications between the devices. Each wireless communication device is only required to administrate the packet number related to the MAC (Media Access Control) address of the AP, because no direct communication is performed between the wireless communication devices.
However, the AP is not present in the ad-hoc mode. Each wireless communication device is required to discriminate all other wireless communication devices in the network, and administrate all packet numbers related to these devices. As a result, a heavy burden is thus placed on each wireless communication device due to the complicated processing.